Version 0.0.0 @ 03:55/08.07.2000

Application Layers: Services

It is possible to run an applications service on nearly any port of a server assuming you have administrative access.

For a nearly complete list of published ports being used for specific services, check out rfc1700.txt.

Some sample default services include

WWW port 80

Telnet port 23

MAIL (SMTP) port 25

FTP port 21

Just because a service's standard port is of one number does not mean that the service must only work on that port. In most cases a system administrator may change the port used by a service too use an alternative that is normally reserved for an entirely different application layer protocol.

For this part, the only item you need to understand is the association of services to standard ports. Clients expect certain services to be available on certain ports. In many cases you as a user cannot modify what ports your client's look to use a service. SMTP (mail) is expected to run run on the same port (25) and many mail programs that accept mail for relay to a mail server only allow you to connect to port 25 on remote machines. This predictable nature for knowing port numbers and their assigned services makes the blocking of outsider users to these services easier with a firewall filter.

A list of well known ports has been extracted from rfc1700.txt for you to see within this document:

Attempts have been made to make the tables appear as they should for LYNX users by forcing a common field width for fields being used by padding them with other printable characters. This is meant to allow for LYNX users to see the tables much like the Netscape and other web browser worlds might show them. However, from personal experience, some versions of LYNX still manage to munge the tables, making them use up several pages. It seems to be a problem with how earlier versions of LYNX dealt with tables, but the problem has not been entirely isolated.

Some have asked why this collection of on-line documents is so lacking of graphic content. To them I answer: faster downloads. Many of these pages are smaller than some pictures on many commercial web sites. You do not come here to look at my pictures. You come here to read content. Also, LYNX users benefit from this, and by using ALL text, people with ADA issues are able to use speech recognition software on the text to hear the words.

A Special License: No part of this document may be used for profit without the consent of the author Michael Egan in writing. Content may be duplicated for retransmission for non-profit purposes as long as the copyright and license remain included in their entirety. The content is provided "as-is" and I take no responsibility on the content's truthfulness or consistency. Errors may exist in these documents, but acting upon these errors is left up to the reader to verify by a third party that will take responsibility for fact verification. When notified of errors or inconsistencies, attempts will be made to rectify the errors.

In plan English this is meant to do many things: This copyright is meant to exist so that others may not profit from this work as published in paper form, or by duplicating the content to place advertisements over it and generate income. It is also meant to exist to prevent people from publishing this work as their own and receiving profit from this process on research they did not perform. It is not meant to stop a professor from running off copies to use in their classes for their students. It is also not meant to stop the student from printing up copies for their own education. How depressing it would be to find your work published in book form without your permission, or compensation. Another reason for this Copyright is to limit the effect of the mistakes I have made within this document before I was able to complete it. It would be even sadder to notice my mistakes in print and criticized before I could resolve them. Eventually, after I finish this work, I may retain copyright, but eliminate the license.